A display device using an organic EL luminescent element has a metal electrode disposed on the rear side of a luminescent layer with respect to an observer. This display device has a problem in that, when external light is present, its display quality is significantly impaired by light reflected at the metal electrode or by reflection of a scenery on the observer side. There is known a technique wherein, for the purpose of preventing reflection from the metal, a circularly polarizing plate serving as an anti-reflection film is used on a front substrate of the luminescent element. The circularly polarizing plate includes a polarizing plate and a phase difference film serving as a ¼ wave plate. There is known a technique wherein an oriented polymer film obtained by stretching a polymer film is used as the phase difference film.
When such a prior-art phase difference film is used as a circularly polarizing film, a favorable anti-reflection effect is obtained only at a certain wavelength at which phase difference is ¼ of the wavelength. However, a favorable anti-reflection effect cannot be obtained over a wide wavelength range such as the visible range of 400 nm to 700 nm. As a result, there occurs a problem of coloration of the reflected light.
Patent Literature 1 discloses that, when an anti-reflection film in which phase differences at wavelengths of 450 nm and 550 nm satisfy the relation |R(450)|<|R(550)| (where |R(450)| and |R(550)| represent the absolute values (nm) of in-plane phase differences at wavelengths of 450 nm and 550 nm) is used as a phase difference film, light reflection from a highly reflective reflection surface, such as a metal electrode incorporated in an electroluminescent display element, can be effectively prevented over a wide wavelength range.